A head massager is used for carrying out a massage on the head of a user, and generally includes a helmet and a massage device. The helmet is worn on the head of the user, and the massage device is disposed on the helmet and is used for achieving a massage on the head of the user. For fit on the heads of the users with various sizes of head circumferences, the helmet generally has a first helmet body and a second helmet body which are movable with respect to each other. Two joints of the first helmet body and the second helmet body are respectively provided with an adjustment device. The adjustment device usually utilizes a gear rack mechanism to drive the first helmet body and the second helmet body to move relative to one another. However, this structure has the following shortages: requiring two adjustment devices, and relatively smaller adjustable range since the two adjustment devices form mutual constraint during adjusting operation.